1. Field of the Invention
The present invention relates to a wiring board and its manufacturing method.
2. Discussion of the Background
A processing element such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and a VRM (Voltage Regulator Module) to supply power for such a processing element are mounted on a wiring board to be used as a computer motherboard, for example. A VRM works as a direct-current power source. Therefore, the output voltage phase and the output current phase of a VRM usually correspond to each other. However, under circumstances such as shortly after a processing element has started operations or at a sudden increase in the load intensity of a processing element, the output current phase is delayed relative to the output voltage phase due to the impedance of a transmission line that connects the processing element and the VRM. In such a case, the power supply for the processing element may be delayed.
Also, the electric current flowing through a transmission line that connects a VRM and a processing element generates a magnetic field with the transmission line as its center. Therefore, if the volume of the electric current flowing through the transmission line changes, a subsequent change in the magnetic field may cause noise in a signal line formed in the wiring board.
In Japanese Patent Publication No. 2002-204075, a wiring board having a center conductor and a ring conductor that surrounds the center conductor is described. The contents of Japanese Laid-Open Patent Application No. 2002-204075 are incorporated herein by reference in their entirety in the present application.